Fix warnings on Win64.

Fix warnings on Win64. 
Set warning level to /W3 and change implicit conversions from size_t
to int. Most "fixes" are simply manifesting the implicit casts or using
a special strlen replacement that returns int.

[Lasse Reichstein, 2009-11-10 16:33:12]

High volume but pretty tedious review. Feel free to redistribute it.

[Lasse Reichstein, 2009-11-10 16:37:41]

http://codereview.chromium.org/390004/diff/1/4
File src/api.cc (right):

http://codereview.chromium.org/390004/diff/1/4#newcode2054
Line 2054: int buf_len = static_cast<int>(prefix_len + str_len + postfix_len);
Woops, cast no longer necessary. Will remove.

[Mads Ager (chromium), 2009-11-11 09:38:46]

LGTM